Progranulin-dependent repair function of regulatory T cells drives bone-fracture healing
Ruiying Chen, Xiaomeng Zhang, Bin Li, Maurizio S. Tonetti, Yijie Yang, Yuan Li, Beilei Liu, Shujiao Qian, Yingxin Gu, Qingwen Wang, Kairui Mao, Hao Cheng, Hongchang Lai, Junyu Shi
Ruiying Chen, Xiaomeng Zhang, Bin Li, Maurizio S. Tonetti, Yijie Yang, Yuan Li, Beilei Liu, Shujiao Qian, Yingxin Gu, Qingwen Wang, Kairui Mao, Hao Cheng, Hongchang Lai, Junyu Shi
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Research Article Bone biology

Progranulin-dependent repair function of regulatory T cells drives bone-fracture healing

Abstract

Local immunoinflammatory events instruct skeletal stem cells (SSCs) to repair/regenerate bone after injury, but mechanisms are incompletely understood. We hypothesized that specialized Tregs are necessary for bone repair and interact directly with SSCs through organ-specific messages. Both in human patients with bone fracture and a mouse model of bone injury, we identified a bone injury–responding Treg subpopulation with bone-repair capacity marked by CCR8. Local production of CCL1 induced a massive migration of CCR8+ Tregs from periphery to the injury site. Depending on secretion of progranulin (PGRN), a protein encoded by the granulin (Grn) gene, CCR8+ Tregs supported the accumulation and osteogenic differentiation of SSCs and thereby bone repair. Mechanistically, we revealed that CCL1 enhanced expression levels of basic leucine zipper ATF-like transcription factor (BATF) in CCR8+ Tregs, which bound to the Grn promoter and increased Grn translational output and then PGRN secretion. Together, our work provides a new perspective in osteoimmunology and highlights possible ways of manipulating Treg signaling to enhance bone repair and regeneration.

Authors

Ruiying Chen, Xiaomeng Zhang, Bin Li, Maurizio S. Tonetti, Yijie Yang, Yuan Li, Beilei Liu, Shujiao Qian, Yingxin Gu, Qingwen Wang, Kairui Mao, Hao Cheng, Hongchang Lai, Junyu Shi

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Figure 5

Macrophage-derived CCL1-mediated CCR8+ Tregs migration into the injury site.

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Macrophage-derived CCL1-mediated CCR8+ Tregs migration into the injury s...
(A) Schematic diagram showing the FTY720 treatment protocol. (B) The fractions of CCR8+ Tregs among total Tregs in the control group (Cntrl) and FTY720-treated group in BM and adjacent lymph nodes at indicated time points. n = 4–5 per group. (C) Transcript levels of chemokine ligand gene transcripts in the wound/callus tissue and control tissue were quantified by qRT-PCR before surgery and on days 3, 7, and 14 after injury. n = 3 per group. (D) Schematic diagram showing CCL1-mediated chemotaxis assay protocol. (E) Representative flow images of the proportions of CCR8+ Tregs among total Tregs in top/bottom chambers treated with CCL1 at indicated concentrations. (F) The number of CCR8+ Tregs in top/bottom chambers treated with CCL1 at indicated concentrations. n = 4 per group. (G) The relative expression levels of Ccl1 in stromal cells, T cells, and macrophages derived from BM tissue in control and bone injury mice. n = 4 per group. (H) Representative images of colocalization of F4/80 (red) and CCL1 (green) in control/injured bone tissue. Scale bars: 10 μm. (I) The relative expression level of Ccl1 in BM macrophages treated with PBS or IL-6. n = 4 per group. All data are shown as mean ± SEM. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.005; ****P ≤ 0.001, as determined by 2-way ANOVA with Bonferroni’s multiple-comparisons test (B, C, and F), 1-way ANOVA with Bonferroni’s multiple-comparisons test (G), or unpaired 2-tailed Student’s t test (I).